The class of polymers of carbon monoxide and olefin(s) has been known for a number of years. Brubaker, U.S. Pat. No. 2,495,286, produced such polymers of relatively low carbon monoxide content in the presence of free radical catalysts, e.g., peroxy compounds. U.K. Pat. No. 1,081,304 disclosed the production of related polymers of increased carbon monoxide content in the presence of alkylphosphine complexes of palladium salts as catalysts. Nozaki extended this process through the use of arylphosphine complexes of palladium salts and certain inert solvents, for example, U.S. Pat. No. 3,694,412.
More recently, the class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon, e.g., ethylene or ethylene and propylene, has become of greater interest, in part because of the greater availability of such materials. The polymers, generally known as polyketones, have been shown to be of the formula --CO--(A)-- where A is the moiety of ethylenically unsaturated hydrocarbon polymerized through the ethylenic linkage. For example, when the polymer is a copolymer of carbon monoxide and ethylene, the polymer is represented by the formula --CO--CH.sub.2 --CH.sub.2 --. A preferred general process for the production of these linear alternating polymers is illustrated by published European Patent Application Nos. 0,121,965 and 0,181,014. The process generally involves a catalyst composition formed from a Group VIII metal selected from palladium, cobalt or nickel, the anion of a non-hydrohalogenic acid having a pKa below 2 and a bidentate ligand of phosphorus, arsenic or antimony. The resulting polymers are relatively high molecular weight thermoplastic polymers having utility in the production of structural articles such as containers for food and drink and parts for the automotive industry.
The polymers are characterized by relatively high melting points, frequently over 200.degree. C., depending upon the molecular weight and the chemical nature of the polymers. A melting point of this magnitude is of value in many applications, particularly when a shaped article is to be subjected to conditions of elevated temperature. However, when a polyketone polymer is subjected to the high temperatures required for melt processing, chemical changes can occur such as crosslinking, chain scission and formation of undesirable degradation products which can cause loss of attractive physical properties. These changes are particularly apparent in the melting point and the percentage of crystalline versus amorphous polymer as measured by differential scanning calorimetry (DSC). It is desirable that polyketone compositions should not undergo changes in physical properties during melt processing procedures. Stabilization of the percent crystallinity and melting point of the polymer is an indication of stabilization of other physical properties.
It would be of advantage to provide polyketone compositions whose melting point is relatively constant throughout one or more melt processing operations. It would be of advantage to provide polyketone compositions whose percent crystallinity has been stabilized against loss during melting-solidification of the polymer composition.